While a number of Western personality and clinical psychologists have explored the adaptive functions of guilt-proneness in relation to a wide variety of behavioural patterns, the investigation of guilt-proneness in the Arabian-Islamic culture remains a neglected field Perhaps one reason for the absence of research dealing with guilt-proneness and its therapeutic application in the Arab world, and in the Saudi culture in particular, is the lack of an empirically-based measure of guilt-proneness. In this study, a new psychometric instrument, the Guilt-Proneness Scale (GPS), has been developed and used to investigate the role of guilt-proneness in inhibiting involvement in deviant behaviour with particular reference to juvenile illicit drug use and offending behaviour in Saudi Arabia. Exploratory factor analysis of the GPS (based on 214 Ss) has revealed three aspects of guilt-proneness phenomenon among Saudi subjects: (1) religious-related guilt (RG), (2) social-related guilt (SOG), and (3) self-oriented guilt (SG). The GPS total and these three subscales have demonstrated satisfactory levels of reliability in terms of both test-retest and internal consistency criteria. A confirmatory factor analysis examination using Structural Equation Modelling techniques (SEM), has confirmed this three-factor model for guilt-proneness. SEM was performed on the data of three subject groups: the first was 206 Ss., the second was 227 Ss., and the third (a combined group) was 433 Ss. Regarding the scale validation, the attempts to establish evidence of the criterion-related, construct, and disciminant validity of the GPS measure of guilt-proneness have been largely successful. The GPS has been utilised in investigating the role of guilt-proneness in inhibiting involvement in illicit drug taking and criminal behaviour of Saudi male juveniles. A study was conducted comparing individual differences in guilt-proneness between voluntarily admitted illicit drug patients (N = 64), convicted illicit drug users (N = 58), non-drug-abusing offenders (N = 71), and normal controls (N = 68). Based on a discussion of current theoretical and empirical approaches dealing with the relationship of guilt-proneness to involvement in illicit drug use and crime, a number of hypotheses were formed. It was hypothesised that: (H1) Normal subjects should manifest greater amount of religious-related guilt than would the voluntary drug abusers, convicted drug abusers, or offenders. (H2) Voluntarily admitted drug abusers should score higher on the three guilt-proneness subscales than would either the convicted drug abusers or the offender group. (H3) Guilt-proneness as measured by the GPS scales should be associated negatively with level of psychopathy. (H4) There should be significant differences in mean guilt-proneness scores among groups varying in their drug preference. (H5) Guilt-proneness in the offender group should be associated negatively with the number of convictions. (H6) The offenders who had committed violent crimes should display significantly lower level of guilt-proneness than those who had been involved in non-violent crimes. In addition to the these hypotheses, the interaction between guilt and selected variables was also examined. The analyses yielded promising results with regard to the measurement of individual differences in guilt predisposition between the groups tested. Both the convicted drug abusers and the non-drug-abusing offenders were marked by low susceptibility to experiencing guilt. Unlike the convicted drug abusers and the non-drug-abusing offenders, the voluntarily admitted drug abusing patients tended to maintain a healthy level of susceptibility to experiencing guilt which is postulated to be significantly influential in their decision to seek treatment. The normal controls manifested the highest religious-related guilt (RG) scale. The findings also revealed that the voluntarily admitted drug patients were distinguished from both the convicted drug takers and the non-drug-abusing offenders. However, no significant differences were found between the convicted drug takers or the offenders. An examination of the relationship of guilt-proneness to psychopathy indicated a significant negative correlation. This pattern of correlation, revealed for the first time for subjects of an Arabian culture, seems in line with most research exploring the relationship of guilt-proneness to psychopathy in Western juveniles. With regard to the examination of the individual difference in guilt-proneness between heroin users, alcohol users, and multi-drug users, it was found that all the three guilt-proneness scales differentiated significantly (p =<0.005) between the three groups of illicit drug taking. In addition, an examination of the relationship between level of guilt-proneness and experience with illicit drug use indicated that those newly involved in taking illicit drugs manifested significantly higher RG, SOG, and SG than the long-term users (p =<0.01). The results of the present study also showed that the RG, SOG, and SG scales differentiated significantly between the recidivists and first time offenders, and between offenders who had committed violent offences and those who had committed non-violent offences. Consistency of the effect of guilt-proneness in inhibiting involvement in deviant behaviour relating to the use of illicit drugs and commission of crimes, has been examined in a 33-month follow-up study. The follow-up study demonstrates that the re-admitted illicit drug patients had significantly lower GPS scores (p =<0.001) than those showing recovery from illicit drug dependence. The results derived by the follow-up also reveal an interesting relationship between relapse (readmission) and having low scores on the three GPS subscales. With regard to the offender group, the results demonstrated a significant correlation (p =<0.01) between the GPS scores of the Recidivists, taken at the time of the first and second testing with a 33 month interval. Hence evidence of the predictability of guilt-proneness as measured by the GPS scales, appears to be very promising. In general, the results of the comparison study as well as the follow-up study provide support for the positive role of guilt-proneness in inhibiting involvement in illicit drug taking and offending behaviour in the Saudi juveniles. In addition, these findings have demonstrated the effectiveness of the GPS as a measure of guilt and in predicting the occurrence of a particular class of behaviour. The final part of the present research was aimed at providing extended individual-case examples of use of the GPS. I have employed a personal construct theory approach through the use of the Repertory Grid technique. Individual GPS profiles, as well as Rep Grid data, were obtained for five in-patient illicit drug abusers and one incarcerated offender. Based on the use of cluster analysis, construct intercorrelation, and principal components analyses, the results of individual grids of each of the six cases were analysed. These demonstrated a pronounced and statistically significant agreement between GPS profiles and Rep Grid indicators of the individual's level of willingness to giving up the use of illicit drugs or involvement in crimes (p =<0.05). These findings demonstrate further the value of guilt-proneness in predicting the individual's response to rehabilitation. They clearly extend support for the GPS as a powerful and useful diagnostic tool. Its use in conjunction with the repertory grid technique with both drug abusers and criminal offenders seems very promising and encourages further research.